The present invention relates to a gripping element for sports shoes, particularly to cleats of a stiffly elastic material which are provided with a projecting insert or rigid, highly abrasion resistant material.
A gripping element of the initially mentioned type is known from German Offenlegungsschrift No. 32 33 900, for example. There, an insert made of oxide ceramics has, in one embodiment, the form of a disk with an outwardly arched tread surface and flat inner surface. At a distance from the flat inner surface, a flat surface of fastening pin is provided. In another embodiment, the insert made of oxide ceramics is formed almost as a pointed cone that is provided with recesses on an inside flange. The flange is coated with plastic and is sunk into the sole.
Another similar cleat insert made of ceramics is known from German Pat. No. 35 32 607 and corresponding U.S. Pat. No. 4,698,924. This insert has the same form as the first mentioned disk, except its inner surface is arched outward slightly and is soldered or glued to a metal fastening element which may be the end of a metal pin or a metal plate or a metal spring end. It is common to all these embodiments that the insert made of ceramics, particularly oxide ceramics, is fastened practically completely rigidly in a cleat-shaped base portion (as is necessary if the soldered or glued connection is not to fracture in use). This applies particularly to the embodiment known from German Pat. No. 35 32 607 and U.S. Pat. No. 4,698,924 in which the ceramic insert is soldered to a pin, and possibly less so to the spring-mounted embodiment.
As is known, ceramics are very abrasion-proof, for which reason this material is especially suitable for gripping elements in certain applications. Ceramics can also withstand very high compression stresses. But ceramics, and also hard alloys, are very brittle, so that they are relatively sensitive to shearing forces and bending forces, and thus are prone to fracturing if rigidly mounted and subjected to the type of forces typically experienced by an athletic shoe cleat.
In U.S. Pat. No. 4,644,672, an outer sole for an athletic shoe is disclosed that has cleats with exchangeable gripping elements that are secured to the sole by being mounted upon studs, of a hard and bending resistant material, which project from the outsole at its ground contacting side. The studs have annular grooves and the gripping elements are in the form of a cap-shaped base that is made of a resilient elastic material and provided with a recess having a shape, with annular ribs, adapted to the outer contour of the stud. As a result, a snap-locking engagement is obtained due to the resiliency of the elastic material of the gripping elements and the mirror-imaged shaping of the stud and recess. Furthermore, to enhance the abrasion resistance of the gripping elements, their tread portion is formed of abrasion resistant material. In particular, a tread portion, in the form of a conical disk or dome made of metal, leather, or a ceramic material, is glued onto the cap-shaped base of the gripping elements and/or is provided with pin-like projections which are inserted or snapped into correspondingly shaped recesses in the cap-shaped base.
While the arrangement of the precedingly described patent is an effective means for providing an athletic shoe sole with exchangeable cleats, the fact that each cleat is formed of three components (a stud, a cap-shaped base, and a tread portion) adds to the cost of producing a sole with such cleats. Furthermore, insuring that the tread portion of rigid material will remain securely fixed to the resilient material of the base portion and not break off in use is not without problems too.
With the present invention, a primary object is, therefore, to form a cleat type gripping element with an insert of the type mentioned wherein the shearing and bending forces occurring on the tread surface cannot lead to the fracturing of the insert material or of its connection to the body of the cleat.
It is a further object of the invention to provide a cleat of abrasion resistant ceramic which is easily and economically producible.
These objects are achieved in accordance with a preferred embodiment of the invention by providing the cleat with an insert of rigid, highly abrasion resistant material of a shape wherein a midsection of the insert has a single constriction that divides the insert into a tread section having a tread surface and a fastening section; wherein the ratio of a maximum diameter of said tread section of the insert relative to the total height of the insert is about 1:0.75 to 1:1.8; wherein the height of constriction is 25% to 60% of the total height of the insert and wherein the smallest diameter of the constriction is 75% to 45% of the maximum diameter of said tread section.
Due to the formation of the cleat insert with a constriction according to the invention, the insert is anchored permanently in the cleat-shaped substructure. Despite this, the insert can be elastically deflected sideways in and with the cleat when strong forces, particularly shearing forces, occur in the edges areas, since the constriction forms a kind of bearing. Thus, for example, with forces acting at an angle of 30.degree. to 70.degree. on the edge, the insert can elastically, flexibly give way so that impact forces or loads can be reduced. Thus the danger of fracturing of the insert material, especially in the edge area of the insert, is greatly reduced. Furthermore, no bonding of the insert to another component is required.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.